Current treatment of solid tumors is limited by inherent tumor resistance to radiation or chemotherapy and by toxicity from systemic administration of antineoplastic agents. Our long-term goal is to overcome these limitations by developing for localized tumors a targeted therapeutic approach that increases the specificity and efficacy of the therapy and reduces the cytotoxicity in normal tissues. We have developed a thermally responsive polypeptide carrier for the chemotherapeutic doxorubicin which inhibits proliferation of cancer cells in culture. Our hypothesis is that after systemic administration these genetically engineered polypeptides can be targeted to the tumor site by applying local hyperthermia. This will result in accumulation of the agent in the tumor with subsequent inhibition of tumor growth. The amino acid sequence of the designed polypeptides is based on elastin-like polypeptide (ELP) biopolymers which are soluble in aqueous solution at physiological temperature (37 [unreadable]C), but aggregate when the temperature is raised above 40 [unreadable]C. The Tat membrane translocating sequence, derived from the HIV-1 Tat protein, known to facilitate delivery of large cargo proteins across cell membranes, is conjugated to the ELP to facilitate cell entry. A tetrapeptide GFLG linker was included at the C-terminus of ELP. This lysosomally degradable peptide linker separates the ELP polypeptide from a cysteine residue that can be coupled to doxorubicin. Our preliminary in vitro results demonstrate a very significant effect of the Tat-ELP-Dox construct in MES-SA and MES-SA/Dx5 multidrug resistant uterine sarcoma cell cells when compared to a non-thermally responsive control peptide. In order to address the hypothesis that Tat-ELP-Dox can be thermally targeted to tumor tissue, the following specific aims will be addressed: (1) Measure the plasma kinetics and in vivo distribution of Tat- ELP-Dox in normal and neoplastic tissue in an athymic rat model by determining the plasma concentration curve and determination of the tissue concentrations with quantitative autoradiography, and (2) Evaluate the therapeutic efficacy of Tat-ELP-Dox in the treatment of neoplastic xenografts in the thigh of athymic rats with and without localized hyperthermia through repeated administration of the agent coupled with local hyperthermia. Specific targeting of the proposed chemotherapeutic polypeptide carrier to solid tumors by local hyperthermia would increase specificity and efficacy of treatment and reduce the cytotoxicity in normal tissues. The successful completion of the proposed research will provide technology which has competitive advantage over existing/alternate technologies and it would provide an alternative mean to effectively substitute or augment present therapy for treatment of localized tumors. Current treatment of solid tumors is limited as only a small fraction of the administered dose of drug reaches the tumor site, while the rest of the drug is distributed throughout the body causing undesirable side effects to normal tissue when drugs are used in the doses required to eradicate cancer cells. Our long term goal is to overcome this limitation by developing an approach that allows the drug to be delivered specifically to the tumor site. This will increase the specificity of the therapy and reduce the toxicity in normal tissues. [unreadable] [unreadable] [unreadable]